1. Field of the Invention
This invention relates to wrapping machines of the type, hereinafter termed the type specified, comprising a tube former for forming a web of wrapping material into a tube with a longitudnal seal, a variable speed feeding mechanism for feeding the web continuously to the tube former, an infeed conveyor for feeding articles in succession into the tube former so that they become entubed in the tube of wrapping material and crimping dies situated beyond the tube former which are operative to form transverse seals in the tube or wrapping material between the articles and, if desired, also to sever it into individual packages.
2. Description of the Prior Art
In existing machines of this type, the crimping dies are normally rotary dies which rotate continuously, at uniform or variable velocity, and produce transverse seals at a regular spacing in the tube. It is, however, possible to use reciprocating dies, which periodically close on the tubes and advance with it to form a seal and then release it, or dies which perform an orbital motion. In all cases the dies of existing machines form a transverse seal in the tube at each machine cycle.
For effective formation of the transverse seals it is necessary that the speed of the crimping dies should be substantially equal to the linear speed of advance of the tube at the moment of sealing, and by this is meant that the speed of the dies must be so matched to the speed of advance of the tube that it is not substantially less than, although it may slightly exceed, the speed of advance of the tube. Rotary crimping dies in existing machines make one revolution per machine cycle, i.e., per revolution of a constant speed driving shaft, and the maximum distance between successive transverse seals, and therefore the maximum length of package which can be made by the machine, is accordingly substantially equal to the circumference of the circle swept by the rotating dies.
If the machine is to be used for wrapping articles which are shorter than the maximum length of package, it is obviously desirable to shorten the package length to avoid wastage of wrapping material. This can be achieved by adjustment of the web feeding means to feed the web more slowly and corresponding adjustment of the infeed conveyor, but provision must then be made for adjusting the peripheral speed of the rotary crimping dies, which continue to make the same number of revolutions per unit of time, during the periods while the transverse seals are being made. This can be achieved by applying to the crimping dies a speed modulating drive, which is adjustable to match the speed of the dies to that of the tube during that portion of the machine cycle at which a transverse seal is formed. Such speed modulation drives are well known and are described, for example, in British Pat. No. 1,420,471 and in U.S. Pat. Nos. 3,633,333 to Schlemmer et al., and 3,546,849 to Zimmerman.
By the provision of such a modulated drive for the rotary crimping dies, the machine can be adapted to wrap articles within a given range of length determined as to its upper limit by the aforesaid maximum package length. With a machine using continuously rotating crimping dies, it is only possible to increase the package length above this maximum by replacement of the dies by larger dies, which sweep a larger circle. This involves the complication and expense of providing a second set of dies and making provision for adjustment of the spacing between the shafts of the dies to accord with the size of die fitted. Also production time is lost during changing of the dies.
The object of the present invention is to provide a universal machine which can be adjusted to suit a much wider range in length of the articles to be wrapped without the necessity for exchange of the crimping dies.